Abstract:
AIM : Mountains are often used to study how environmental factors influence
biodiversity. However, we have limited understanding of the processes causing
biodiversity variation in mountains and whether such processes vary across
trophic levels and spatial scales. The aim of this study was to evaluate (i) whether
community assembly processes varied along elevational gradients, (ii) whether there
were differences in such variation between primary producers (vascular plants) and
secondary consumers (spiders) and (iii) whether there were scale dependencies in any
elevational variation in community assembly.
LOCATION : Fennoscandia, Northern Sweden.
TAXON : Vascular plants, spiders.
METHODS : We used phenotypic and phylogenetic dispersion to quantify how elevation
influenced community assembly of vascular plants and spiders and whether there
were any scale dependencies in such influences. Our original data of plant and spider
communities came from our own field surveys, phenotypic dispersion was calculated
based on matrices of ecological traits, and phylogenetic dispersion was calculated
from phylogenetic trees for each organism group. Trait matrices were based on
a combination of literature values and our own measurements. The phylogeny for
vascular plants was based on a published plant super-tree,
whereas the phylogeny for
spiders was created by ourselves based on the DNA sequences at the mitochondrial
cytochrome c oxidase subunit 1 (COI).
RESULTS : Plants were environmentally filtered throughout all elevations and scales,
but the importance of convergent evolution increased with elevation. For spiders, the
importance of environmental filtering as well as niche conservatism increased with
elevation. For both groups, communities at smaller scales were more influenced by
biotic regulation and niche conservatism than at larger scales.
MAIN CONCLUSIONS : Our study highlights both taxonomic differences and scale
dependencies in how elevation influences community assembly. We argue that these
results can have broad ramifications for our understanding of how spatial variation
in biodiversity is generated and maintained. This may have particular relevance for
our ability to predict the ecological consequences of climate change. Our results further highlight that high elevation specialists may suffer increased risks of climate
driven extinctions due to a combination of increased competition and increased
fragmentation of suitable habitats. Particularly for spiders, which had high elevation
specialists clustered along specific lineages, such extinctions could lead to significant
loss of phylogenetic variation.
